Novel single-step hydrophobic modification of polymeric hollow fiber membranes containing imide groups : its potential for membrane contactor application

Abstract

Highly hydrophobic surface property of membranes is very important for membrane contactor application that is normally used for CO2 capture. This study explores a simple and inexpensive approach for hydrophobic modification of imide group contained polymeric membranes. Poly(amide–imide) (PAI) hollow fiber membrane with controlled pore structure as porous substrate was fabricated by dry-jet wet spinning process, followed by a wet-chemical hydrophobic modification using octadecylamine. The modification mechanism was confirmed by ATR-FTIR, and the effect of different modification times on the modified membrane properties was investigated. Experiments reveal that the modification changed the membrane morphology and structure, resulted in surface pore opening and thinning down of the membrane skin layer. As a compromise between the membrane hydrophobicity and mechanical strength, 10–30 min were considered as appropriate modification times for the PAI membranes. The treated membranes showed much higher hydrophobicity with an improvement in contact angle of around 30°. The liquid entry pressure (LEPw) also increased dramatically from 7 psi to 63 psi after 30 min modification due to the enhanced membrane hydrophobicity. The treated membranes were tested in the membrane contactor for CO2 absorption. It was observed the CO2 flux increased with the liquid velocity and modification time. A stable long-term performance of CO2 absorption by a 2 M sodium taurinate aqueous solution for 15 days of operation was attained. Moreover, poly(etherimide) (PEI) hollow fiber membranes were successfully modified by octadecylamine, which demonstrated the effectiveness and versatility of the modification method on imide-contained polymeric membranes.